Fuel burner



F L.. HEMKER sept. 1o, 196s FUEL BURNER Filed Oct. 6, 1965 INVENTORFritz L. Hemker ATTORNEY United States Patent 0 3,400,921 FUEL BURNERFritz L. Hemker, Wadsworth, Ohio, assigner to The Babcock & WilcoxCompany, New York, N.Y., a corporation of New Jersey Filed Oct. 6, 1965,Ser. No. 493,458 11 Claims. (Cl. 266-29) ABSTRACT 0F THE DISCLOSURE Aburner arrangement whereby the major portion of an ash containing fuelis burned in a combustion chamber prior to introduction into a blastfurnace. This is accomplished by radially introducing all of thecombustion air into the chamber through a plurality of regularly spacedopenings covering the circumferential area of the combustion chamber.This radially introduced air forms a protective layer of air between thefuel stream and the inner surface of the combustion chamber thusprotecting the chamber walls from the intense heat required forachieving this more complete burning of the fuel.

This invention relates generally to fuel burners and more particularlyto a fuel burner specifically adapted for firing coal or other solidcarbonaceous fuel in a blast furnace.

The merits of firing supplemental fuel in a blast furnace to decreasecoke consumption are well known; moreover, it is generally appreciatedthat thermodynamically, coal is superior to oil or gas for this purpose.Recent experimental operation of a blast furnace using coil injectionhas indicated however that when coal is introduced into a blast furnaceat high rates, heavy carry-over of carbon in the top gas results. Thiscarry-over is believed to result from the hot blast air reactingpreferentially with the coke in the blast furnace in lieu of reactingwith the injected coal which is at a lower temperature. As aconsequence, the hydrocarbons in the unburned coal break down intohydrogen and carbon fractions in the high ternperature reducingatmosphere of the blast furnace, with the carbon being carried over withthe top gas. These recent experiments indicate that if coal is to beused as a supplemental fuel in blast furnaces, for economic operation itwill have to be almost completely burned or at least devolatilizedbefore being admitted to the blast furnace. This would require a fuelburner capable of containing the combustion process without beingsubject to slag accumulations. Moreover, since it is desirable to It istherefore an object of the present invention to provide a fuel burner,specifically adapted for burning particle-form carbonaceous fuel, suchas pulverized coal, in a blast furnace, wherein a major portion of thefuel is burned within the burner itself prior to discharge into theblast furnace. It is a further object of the present invention that suchburner be capable of operation without requiring water cooling of anytype other than what is normally used in the vicinity of blast furnacetuyeres of present day design. It is a still further object of thepresent invention that the fuel burner be structurally adaptable forincorporation into existing blast furnaces.

These and other objects may be attained in a blast furnace having aboundary wall formed with a tuyere opening and a fuel burner arranged tofire through the tuyere opening. The burner includes an elongatedrefractory burner tube of generally circular cross-section in axial3,400,921 Patented Sept. 10, 1968 alignment with the tuyere opening andhaving an inlet end and an open discharge end. The burner tube is formedwith a plurality of relatively small, spaced openigs over substantiallyits entire inner surface, and is enclosed with in a windbox chamber towhich high temperature blast air is delivered. A fuel stream containingparticle-form carbonaceous fuel is introduced into the inlet end of theburner tube. The pressurized blast air supplied to the windbox chamberpasses through the burner tube open ings and mixes with and burns amajor portion of the fuel within the burner tube prior to discharge ofthe hot combustion products into the blast furnace. The openings in theburner tube are sized and arranged to insure an adequate, positiveinflow of air through all of the openings during burner operation toeffect a protective layer of air between the intensely hot burning fuelstream and the inner surface of the burner tube.

For a better understanding of the invention, its operating advantagesand specific objects attained by its use, reference should be had to thefollowing description which refers to the accompanying drawing in whichFIG. 1 is a sectional side elevation of a fuel burner according to thepresent invention mounted in the boundary wall of a blast furnace.

Referring to the drawing7 a burner 10 according to the present inventionis mounted to fire into the upper hearth area of a blast furnace chamber12 which is cylindrical in horizontal cross-section and is bounded by arefractory wall 14 encased on its outside by a metallic shell plate 16.The burner 10 is mounted on a flange member 17 which is suitably weldedto the plate 16 and circumscribes the outer periphery of an inwardlytapered tuyere opening 18. A water-cooled inwardly tapered frustoconicaltuyere cooler casting 20 lines the inner surface of the tuyere opening18. Suitable connections 20A and 20B are provided for effecting thecirculation of cooling water through the tuyere cooler casting 20. Awater-cooled tuyere 22 projects into the furnace chamber 12 and engagesat its rearward end with the forward end of the tuyere cooler casting20. Suitable threaded connections 22A and 22B are provided for thecirculation of cooling water through the tuyere 22. The inner wall ofthe tuyere 22 defines an unobstructed discharge passage or port 24 thatis axially aligned with the tuyere opening 18. The

above-described tuyere opening 18 and water jacketed members 20 and 22are of standard blast furnace construction.

The burner 10 includes a windbox casing 26 enclosing a windbox chamber28. The casing 26, the forward end of which fits within the recessformed by the tuyere cooler casting 20, includes an inwardly taperedfrusto-conical wall portion 29 which is spaced from and substantiallyparallel with the inner wall of the tuyere cooler casting 20, an innerend plate 30 that is formed with an opening axially aligned with theydischarge passage 24 of the tuyere 22, and an outer end plate 31. Theouter end plate 31 engages a flanged portion of a tuyere stock elbow 32,the elbow 32 being connected for flow of high temperature blast airtherethrough from a bustle pipe (not shown) of the usual type common toblast furnaces. The inner walls of the elbow 32 and the casing 26 arelined with heat resistant refractory material 33, in view of the factthat the blast air flowing through the elbow 32 into the windbox chamberis normally in the order of 1800- 2000 F.

At the junction 30A of the inner flange plate 30 and the tuyere 22, andat the junction 31A of the outer end plate 31 and the elbow 32, theengaging surfaces are spherical in shape so `as to allow nominal amountsof relative movement between the elbow 32, windbox casing 26 and tuyere24. These elements are maintained in proper position by means of aspring tensioned bridle assembly 33 which resiliently interconnects abracket 34 rigidly attached to the elbow 32 with the shell plate 16.

The main component of the burner is an elongated cylindrical burner tube40 that is 'arranged within the windbox chamber 28 and has its centralaxis in alignment with the axis of the discharge port 24 of the tuyere22. The bumer tube 40 is positioned and supported by means of radiallyprojecting struts 45 attached at their inner ends to a pair of spacedsupport rings 46 which embrace the tube 40 and at their outer ends tothe windbox casing 26. The forwardmost end of the tube 40 is maintainedin ialignment with the tuyere port 24 by means of ra support ring 47which is wel-ded to the inner end plate 30 and embraces the end of thetube 40. The outer (inlet) end of the burner tube 40 is closed by acircular plate 42, and the open discharge end is in direct communicationwi-th, and the same diameter as, the discharge passage 24 of the tuyere22. The burner tube 40 is formed over its entire cylindrical area with aplurality of substantially regularly spaced openings 41, the details ofwhich will be discussed here- 'inaften Projecting rearwardly from theelbow 32 is an access tube 35 which is closed at its end by a removableplate 36. A shielding tube 37 extends through and is welded to the plate36. Extending within the shielding tube 37 is a fuel supply pipe `44which has its open discharge end projecting through the plate 42 so thata fuel stream is introduced into the burner tube generally along itsaxis. The function of the shielding tube 37 is to prevent overheating ofthe fuel in the supply line 44 by the hot blast air owing through theelbow 32. The outer end of the shielding tube 37 is closed by a seal cap38 through `which the fuel pipe 44 passes. The fuel pipe 44 connectswith a fuel source (not shown).

A sighting tube 39 is welded to and extends through the plate 36 andinto the burner tube 40 so that combustion conditions can be visuallymonitored.

The fuel to be delivered to the above-described burner 10 via pipe 44 ispreferably pulverized coal in dense phase transport, i.e. pulverizedcoal entrained in a stream of carrier gas, the mixture having 'a carriergas to solids ratio no greater than 5 cubic feet of carrier gas (atstandard conditions) for each pound of solids. A preparation andconveying system for delivering such a dense phase coal stream to ablast furnace is disclosed in U.S. -Patent 3,204,942, issued Sept. 7,1965, in the name of I H. Kidwell et al. 'It is contemplated that thephase dense phase transport will also include a solid fuel/ liquidslurry, e.g. a mixture of pulverized coal and fuel oil. It is furtherintended that crushed as well as pulverized coal or char entrained in -acarrier fluid be within the purview of the present invention, and thephase particle-form carbonaceous fuel is used herein as being inclusiveof these forms of lfuels.

-In the operation of the burner 10, hot blast air is supplied to thewindbox 28 via elbow 32, and coincidentally a stream of fuel isintroduced axially into the burner tube 40 through pipe 44. The air,after passing through the openings 41, mixes with lthe fuel, and sincethe blast air temperature is Well above the ignition temperature of someof the fuel stream components, ignition takes place within the burnertube almost immediately. By properly spacing yand sizing the openings 41in the burner tube 40, air is introduced into the tube along its entirelength so that a substantial portion of the fuel is burned before-discharge into the blast furnace chamber 12.

The sizing of the burner tube 40 and openings 41 is critical in thedesign of this burner. As above stated, ya substantial amount ofcombustion takes place within the |burner tube 40, and it should berecognized that the combustion gas temperatures resul-ting from thisburning approach temperature levels of 4000 F. By properly sizing theburner tube 40 and the openings 41, it has been found that a protectivelayer of air can be maintained along the entire inner surface of theburner tube 40 .to prevent impingement of the hot gases on the innerwall of the burner tube 40. rFhis same influx of air along the entirelength of the 'burner tube 40 also prevents the deposition of slag onthe inner wall of the tube. It should be noted that the windbox chamber28 is forwardly tapered to enhance the distribution of air to theopenings 41 along the length of the burner tube 40.

An experimental burner of the type Idescribed above has been operated inthe test facilities of the assignee of the present invention todetermine the design perimeters and limitations of this burner. In thetest burner, the burner tube 40 was 341/2 inches long and 6 inches(inside) in diameter. Satisfactory operation was obtained by providingevenly spaced openings 41, the cumulative area of which was between 6and 7% of the total area of the inner surface of the burner tube 40. Asa result of these tests, it was concluded that the ratio of cum-ulativearea of the spaced openings 41 to the area of the discharge area at theend of the tube 40 should lbe no greater than approximately 1.5. Thehigher ratios were found to result in llame impingement on the burnertube 40 and its rapid failure. The lower ratios were found to beoperable; lhowever, excessive pressure drop resulted. It was `furtherfound that the diameter of the openings 41 should not exceedapproximately 3/s-inch, since large openings resulted in excessivespacing between openings with consequent breaking down of the layer ofcooling air `and localized hot spots between openings.

Both a stainless steel burner tube and a ceramic burner tube were testedduring the abovedescribed experimental operation of this burner. Thestainless steel tube demonstrated good characteristics in that it waslight and structurally adequate; however, it has an obvious limitationof about 1800 F. blast air temperautre. Burning within the ceramicrefractory tube was observed to be slightly superior, probably becauseof better mixing of the fuel and air due to the jet action imparted tothe air because of the increased thickness of the ceramic tube wall.

Calculations indicate that burners according to the present invention,as described above, can be installed in existing blast furnaces withoutany major redesign or rearrangement of equipment, and without anyappreciable increase in pressure drop over what is normally experiencedthrough a blast furnace tuyere opening.

What is claimed is:

1. A fuel burner comprising an elongated burner tube of generallycircular cross-section having a closed inlet end and an open dischargeend, said burner tube being formed over substantially its entire areawith a plurality of substantially yregularly spaced openings, saidopenings being arranged to direct air substantially radially into saidburner tube, wall means enclosing said burner tube to form thereabout awindbox chamber, said windbox chamber being an annular chamberdiminishing in cross-section in the direction of the discharge end ofsaid burner tube, means for supplying air to said burner tube, means forsubstantially axially introducing into the inlet end of said burner tubea stream of ash containing fuel, and means for introducing all of saidair into said windbox chamber to mix with and burn said fuel within saidburner tube, the openings in said burner tube being sized and arrangedto provide a positive inflow of air through all of said openings whensaid burner is in operation so as to provide a protective layer of airbetween the burning fuel stream and the inner surface of said burnertube.

2. A fuel burner according to claim 1 wherein said fuel stream is adense two-phase mixture, one phase of which includes particle-formcarbonaceous fuel.

3. A fuel burner according to claim 2 wherein means are provided forpreheating said air to a temperature above the ignition temperature ofsaid fuel stream, and wherein said burner tube is formed of a heatresistant refractory material.

4. A fuel burner according to claim 2 wherein said burner tube iscylindrical.

5. A fuel burner according to claim 3 wherein the cumulative open areaof the `openings in said burner tube is no greater than approximately1.5 times the area of the discharge opening of said burner tube.

6. In combination, a blast furnace having a boundary wall formed with atuyere opening, a fuel burner arranged to lire through said tuyereopening, means for supplying a stream of ash containing fuel to saidburner, means for supplying blast air to said burner, and means forpreheating said yblast air to a temperature greater than the ignitiontemperature of said fuel, said fuel burner including an elongated burnertube of generally circular cross-section having a closed inlet end andan open discharge end and being in axial alignment with said tuyereopening, said burner tube being formed over substantially its entirearea with a plurality of substantially regularly spaced openings, saidopenings being arranged to direct air substantially radially into saidburner tube, wall means enclosing said burner tube to form thereabout aW-indbox chamber, said windboX chamber being an annular chamberdiminishing in cross-section in the direction of the discharge end ofsaid burner tube, means for substantially axially introducing saidstream of fuel into the inlet end of said burner tube, and means forintroducing all of said blast air into said Windbox chamber to passthrough the burner tube openings and mix with and burn a major portionof said fuel within said burner tube prior to discharge therefrom, theopenings in said burner tube being sized and arranged to provide apositive inflow of air through all of said openings when said burner isin operation so as,

to provide a protective layer of air between the burning fuel streamland the inner surface of said burner tube.

7. The `combination according to claim 6 wherein said fuel stream is adense two-phase mixture, one phase of which includes particle-formcarbonaceous fuel.

8. The combination according to claim 7 wherein said burner tube isformed of a heat resistant refractory material.

9. The combination according to claim 8 wherein said burner tube iscylindrical.

10. The combination according to claim 9 wherein the cumulative openarea of the opening in said burner tube is no greater than approximately1.5 times the area of the discharge opening of said burner tube.

11. The combination according to claim 10 wherein the cumulative openarea of the openings in. said burner tube is approximately 6-7% of theinternal surface area of said -burner tube.

References Cited UNITED STATES PATENTS 1,450,229 4/ 1923 Robinson.609,744 8/ 1898 Hennig. 2,725,929 12/ 1955 Massier. 3,209,810 10/ 1965Schuvart 266-*29 X FOREIGN PATENTS 351,768 7/ 1931 Great Britain.

I. SPENCER OVERHOLSER, Primary Examiner. E. MAR, Assistant Examiner.

